Take it from someone who used to have zero confidence. :-)
I used to be about a size fourteen which I know isn't exactly huge but still made me feel really bad about myself, especially since I spent my days dancing next to size eights! I then lost about two stone in a few months which now makes me a size ten - twelve. I've got loads more confidence now and love performing in the center.
You actually don't sound 'fat' to me, but if you're serious about losing weight then it's all about motivation. I have a lot of motivation when it comes to studying and thought there was no reason I couldn't use that to lose weight. It seems like you worked really hard to get into university so you must have amazing motivation which you can use. You don't have to do boring tasks like going to the gym and eating things you really don't like. Just cut out things like chocolate, crisps and fizzy drinks completely and swap them for low calorie/fat alternatives. You could also take up a class which you'd enjoy, aerobics or zumba is a really good way to lose weight and it's enjoyable to.
As for freshers week? Seriously, there is nothing to worry about! I can guarantee there will be people much bigger. Plus, it's the first week at university, people aren't going to be going around judging people on their weight! You've worked hard to get to university and you really deserve to get the most out of it, nobody can tell you otherwise.
I wish you all the luck in the future. :-)